Chapter 6 - Exchange Flashcards
How do microorganisms obtain nutrients and remove waste?
- Exchange via their surface
- Nutrients moves in by diffusion
- Waste moves out by diffusion
Why can microorganisms afford to perform exchange via their surface?
- Large surface area to volume ratio
- Short diffusion distance to all cells
- Low demand
Why can’t animals and plants perform exchange via their surface?
- Small surface area to volume ratio
- Multicellular so there is a large diffusion pathway and high demand
- Impermeable surfaces (to prevent pathogens) so require specialised exchange and transport systems
Distinguish between exchange system and transport system
An exchange system increases the rate of diffusion and a transport system delivers nutrients and removes waste from all cells
Summarise the structure of gills in fish
- Fish have many gill filaments and gill lamellae for a large surface area
- Gill lamellae have a thin wall so are permeable and have a short diffusion pathway
Give the features of a specialised exchange surface
- Large compared to volume
- Thin so diffusion distance short
- Selectively permeable to allow selected materials to cross
- Movement of the environmental medium away to maintain concentration gradient
- Transport system to move internal medium to ensure concentration gradent maintained
What is the equation for diffusion
(SA x Difference in conc.) / Length of diffusion path
Summarise the structure of the tracheal system
- Openings on body surface called spiracles
- Valves open to allow gas exchange or close to prevent water loss
- Spiracles connect to trachea
- Trachea connect to tracheoles
- Tracheoles connect to respiring cells and deliver O2, remove CO2
What are the three ways in which respiratory gases move in and out of the tracheal system?
- Along diffusion gradient as O2 is used and CO2 produced
- Mass transport as insects squeeze trachea enabling mass movement of air in and out
- Ends of tracheoles filled with water. Lactate from anaerobic respiration occurs lowering water potential. Water moves from tracheoles due to osmosis and pulls air in due to decrease in volume. Final diffusion also in gas so more rapid
Define countercurrent flow
A mechanism by which the efficiency of exchange between two substances is increased by having them flow in opposite directions ensuring a maximum oxygen gradient is maintained across the full length of the lamellae
How is the structure of a leaf similar to that of an insect
- All cells close to external air and hence a source of oxygen and carbon dioxide
- Diffusion takes place in the gas phase making it more rapid than in water
What are the functions that help gaseous exchange occur in leaves?
- Small pores called stomata ensure no cell far from external air so diffusion pathway short
- Numerous interconnecting air spaces occur in mesophyll so gases come into contact with mesophyll
- Large SA of mesophyll for rapid diffusion
How are stomata controlled and why?
- Controlled by guard cells
- Control rate of gaseous exchange and close stomata to prevent water loss
How have insects evolved to reduce water loss?
- Small SA:V ratio
- Waterproof coverings of a rigid outerskeleton of chitin covered in waterproof cuticle
- Spiracles that can be closed
How do plants limit water loss and why?
- Cover leaves with waterproof coating
- Cannot have small SA as need to photosynthesise
Define xerophytes
Plants adapted to living in areas where water is in short supply
State and describe xerophyte modifications
- Thick cuticle = To reduce water loss
- Rolling up of leaves = Traps regions of water with high water potential so no gradient
- Hairy leaves = Hairs trap moist air with high water potential so no gradient
- Stomata in pits or grooves = Trap moist air next to the leaf reducing water potential gradient
- Reduced SA:V ratio = Reduces water loss as less area
Why do mammals need to remove/obtain large amounts of gases?
- Large organisms with many cells
- High temperature so high respiratory and metabolic rates
Why are lungs located in the body?
- Air is not dense enough to support and protect
- The body would lose water
Summarise the components of the human gas exchange system
- Trachea
- Bronchi
- Bronchioles
- Alveoli
Describe the process of inhalation
- External intercostal muscles contract
- Rib cage moves up and out
- Diaphragm contracts and flattens
- Increase in thorax volume, decrease in pressure
- Air moves in
Describe the process of exhalation
- Internal intercostal muscles contract
- Rib cages moves down and in
- Diaphragm relaxes and bends back to a dome shape
- Volume of thorax decreases so pressure increases
- Air pushed out and aided by elastic recoil of alveoli
What is the formula for Pulmonary ventilation
PV = Tidal volume x Ventilation rate
Tidal volume = Air breathed in/out in one breath
Ventilation rate = Number of breaths a minute
PV = Volume of air breathed in/out per minute
Describe and explain diffusion of gas between alveoli and the blood
- Red blood cells slowed as they pass through pulmonary capillaries allowing more time for diffusion
- Distance between alveolar air and red blood cells reduced as cells flattened against wall
- Wall of alveoli and capillary thin so short diffusion pathway
- Alveoli and capillaries large SA
- Breathing ventilation and heart rate maintains concentration gradient
